1. Field of the Invention
The present invention relates to an optical apparatus that includes an optical semiconductor device and a lens assembly mounted on opposite surfaces of a substrate, and to a method for making the optical apparatus.
2. Description of the Related Art
Precise electrical connections and light transmission paths are crucial to the performance of an optical apparatus. Accordingly, there is a need to mount components of the optical apparatus precisely on a substrate such that the optical apparatus can receive light properly and generate accurate electrical signals.
Referring to FIG. 1, a conventional optical apparatus 1 is shown to include a substrate 100, an optical semiconductor device 19, and a lens assembly 16.
The substrate 100 has a first surface 101, a second surface 102 opposite to the first surface 101, and a plurality of lead holes 200 extending through the first and second surfaces 101, 102 of the substrate 100.
The optical semiconductor device 19 includes a semiconductor package 13, a lead frame 11, an optical semiconductor chip 12, and a plurality of bonding wires 14.
The semiconductor package 13, which is injection molded from plastic materials, includes a base wall 131, a surrounding wall 132 extending from a periphery of the base wall 131 and cooperating with the base wall 131 to form a chip-receiving space 17, and a cover 15 disposed opposite to the base wall 131 and secured to the surrounding wall 132 for closing the chip-receiving space 17. The cover 15 has a wall-connecting surface 152 connected to the surrounding wall 132, and is formed with a light-guiding portion 151 that permits passage of light into the chip-receiving space 17.
The lead frame 11 is made of metal, and includes a chip carrier 111 mounted on the base wall 131 in the chip-receiving space 17, and a plurality of leads 112. Each of the leads 112 has a chip-connecting portion 114 disposed in the chip-receiving space 17, and a substrate-connecting portion 115 extending through the surrounding wall 132 and to be mounted on the substrate 100 in a respective one of the lead holes 200, such as by soldering, so as to secure the optical semiconductor device 19 on the substrate 100.
The optical semiconductor chip 12 has a carrier-mounting portion 113 and a light-sensing portion 121 opposite to the carrier-mounting portion 113. The carrier-mounting portion 113 is mounted on the chip carrier 111 of the lead frame 11 such that the light-sensing portion 121 is optically aligned with the light-guiding portion 151 of the cover 15 when the cover 15 is secured to the surrounding wall 132.
The bonding wires 14 are metal wires and are used to wire-bond the optical semiconductor chip 12 to the chip-connecting portions 114 of the leads 112, respectively, before the cover 15 is secured to the surrounding wall 132.
The lens assembly 16 includes a lens frame 161 and a lens set 162 mounted in the lens frame 161. The lens frame 161 is mounted on the second surface 101 of the substrate 100 such that the lens set 162 is optically aligned with the light-guiding portion 151 of the cover 15, thereby permitting light from the lens set 162 to pass through a light passage 201 in the substrate 100 and the light-guiding portion 151 of the cover 15 for reception by the light-sensing portion 121 of the optical semiconductor chip 12 so that corresponding electrical signals can be generated accordingly.
During the manufacture of the optical apparatus 1, an optimum optical distance is required to be formed between the lens set 162 and the light-sensing portion 121 of the optical semiconductor chip 12 in order for the optical apparatus 1 to generate electrical signals accurately. However, since the lens assembly 16 is mounted on the substrate 100, the depth of the substrate-connecting portion 115 of each of the leads 112 extending through the respective one of the lead holes 200 has to be precisely controlled before installing the lens assembly 16.
Therefore, when making the conventional optical apparatus 1, the distance between the light-guiding portion 151 of the cover 15 and the optical semiconductor chip 12 has to be measured. Then, a rectangular frame 2 is prepared, the height of which corresponds to the difference between the optimum optical distance between the lens set 162 and the light-sensing portion 121 of the optical semiconductor chip 12 and the measured distance between the light-guiding portion 151 and the optical semiconductor chip 12. Accordingly, the rectangular frame 2 has a top surface 22 and a bottom surface 23 opposite to the top surface 22. The top surface 22 abuts directly against the first surface, 101 of the substrate 100, whereas the bottom surface 23 abuts directly against the cover 15.
The method for making the optical apparatus 1 begins with the preparation of the substrate 100, the optical semiconductor device 19, and the lens assembly 16. To prepare the optical semiconductor device 19, the optical semiconductor chip 12 is first mounted on the chip carrier 111 of the lead frame 11. Then, the base wall 131 and the surrounding wall 132 of the semiconductor package 13 are formed on the lead frame 11 by injection molding such that the chip carrier 111 is mounted on the base wall 131 in the chip-receiving space 17, and such that the substrate-connecting portions 115 of the leads 112 extend through the surrounding wall 132. Next, the optical semiconductor chip 12 is wire-bonded to the chip-connecting portions 114 of the leads 112. Finally, the cover 15 is mounted on the surrounding wall 132 to close the chip-receiving space 17. The light-guiding portion 151 of the cover 15 is optically aligned with the light-sensing portion 121 of the optical semiconductor chip 12 at this time.
When assembling the optical semiconductor device 19 and the lens assembly 16 on the substrate 100, a skilled artisan has to first install the rectangular frame 2 such that the top surface 22 of the rectangular frame 2 abuts directly against the first surface 101 of the substrate 100 and such that the bottom surface 23 of the rectangular frame 2 abuts directly against the cover 15. The substrate-connecting portion 115 of each of the leads 112 is then inserted through the respective lead hole 200 in the substrate 100. Next, the unfinished optical apparatus 1 is turned 180° to commence soldering of the substrate-connecting portions 115 of the leads 112 to the substrate 100 so as to establish electrical connection between the optical semiconductor device 19 and the substrate 100 and so as to secure the optical semiconductor device 19 on the substrate 100. The lens frame 161 of the lens assembly 16 is secured to the second surface 102 of the substrate 100 thereafter such that the light-guiding portion 151 of the cover 15 is optically aligned with the lens set 162. The optical apparatus 1 is completed at this time.
Although the presence of the rectangular frame 2 can assure the optimum optical distance between the lens set 162 and the light-sensing portion 121 of the optical semiconductor chip 12, there are some drawbacks that have to be resolved. Particularly, processing errors inherently present in the top and bottom surfaces 22, 23 of the rectangular frame 2 can result in improper optical alignment among the lens assembly 16, the light-guiding portion 151 of the cover 15, and the light-sensing portion 121 of the optical semiconductor chip 12, thereby affecting the accuracy of the electrical signals generated by the optical semiconductor chip 12. In addition, there is a need to prepare rectangular frames 2 of different sizes since a particular lens assembly 16 will require a specific size of the rectangular frame 2. This not only increases the production costs, but also raises another problem due to possible use of an incorrect rectangular frame 2, which can result in malfunction of the optical apparatus 1.